The Protein-Protein Interactions Core Facility combines the complimentary strengths of the Surface Plasmon Resonance Laboratory and the Analytical Ultracentrifugation Laboratory, each of which provides rigorous quantitative analysis of macromolecular interactions and dynamic behavior of complex systems. The Protein-Protein Interactions Core Facility is located within the UTHSCSA Department of Biochemistry. The Surface Plasmon Resonance Laboratory occupies a 400 square foot room, and the Analytical Ultracentrifugation Laboratory occupies an adjoining 400 square foot room. The Surface Plasmon Resonance Laboratory consists of two Biacore 3000 surface plasmon resonance instruments and ancillary computers. The instrumentation?s strengths include speed, sensitivity, small sample consumption and, most importantly, the binding events are measured as they occur in real time. Thus, precise information on the kinetics and affinity of the binding interactions can be determined without the need for purified proteins or detection labels. The Analytical Ultracentrifugation Laboratory consists of three Beckman XL-I analytical ultracentrifuges and ancillary computers. Each analytical ultracentrifuge is equipped with both interference and absorbance optical systems for detecting sedimentation of samples during real time. In addition, funds have recently been obtained to add a fluorescence optical detection system to one of the existing analytical ultracentrifuges. The analytical ultracentrifuge can examine sample purity, detect and characterize conformational changes, determine subunit stoichiometries, characterize assembly and disassembly mechanisms of supramolecular assemblies, and measure equilibrium constants and thermodynamic parameters for associating systems. This information is critically important for understanding macromolecular interactions involved in the molecular basis of cancer.